Various hybrid powertrain architectures are known for managing the input and output torques of various prime-movers in hybrid vehicles, most commonly internal combustion engines and electric machines. Series hybrid architectures are generally characterized by an internal combustion engine driving an electric generator which in turn provides electrical power to an electric drivetrain and to a battery pack. The internal combustion engine in a series hybrid is not directly mechanically coupled to the drivetrain. The electric generator may also operate in a motoring mode to provide a starting function to the internal combustion engine, and the electric drivetrain may recapture vehicle braking energy by also operating in a generator mode to recharge the battery pack. Parallel hybrid architectures are generally characterized by an internal combustion engine and an electric motor which both have a direct mechanical coupling to the drivetrain. The drivetrain conventionally includes a shifting transmission to provide the necessary gear ratios for wide range operation.
Electrically variable transmissions (EVT) are known which provide for continuously variable speed ratios by combining features from both series and parallel hybrid powertrain architectures. EVTs are operable with a direct mechanical path between an internal combustion engine and a final drive unit thus enabling high transmission efficiency and application of lower cost and less massive motor hardware. EVTs are also operable with engine operation mechanically independent from the final drive or in various mechanical/electrical split contributions thereby enabling high-torque continuously variable speed ratios, electrically dominated launches, regenerative braking, engine off idling, and multi-mode operation.
It is known in the art of vehicular powertrain controls to interpret an operator's request for torque into a system torque command to effect an output torque to the vehicle driveline. Such interpretation and command require relatively simple control management dominated by the available engine torque in relation to a vehicle's present set of operating parameters, which relationship is relatively well understood. In electrically variable transmission based hybrid powertrains a number of factors in addition to the available engine torque affect the output torque that can be provided to the vehicle driveline. It is known in such hybrid powertrains to interpret an operator's request for torque into a system torque command and allow individual sub-system limitations to dictate actual output torque. Such limitations include, for example, available engine torque, available electric machine torque and the available electrical energy storage system power. It is preferable to understand the various subsystem individual and interactive constraints affecting available powertrain output torque such that output torque commands are issued consistent with such torque availability and subsystem constraints.
Available development tools and modeling may provide some understanding of electrically variable transmission based hybrid powertrain available output torque. But such techniques are generally limited to steady state operation, neglecting the significance of inertia torques upon the powertrain from vehicle dynamic conditions including vehicular and powertrain (engine and electric machine) accelerations. Such techniques are also generally iterative in nature and rely on human intervention is determining what parameters are held constant and what parameters are to be solved for. Such techniques, therefore, are ill equipped for adaptation to real-time, on-vehicle, dynamic, multi-variable solutions for effective control.